How long could you keep a medium sized, brown, healthy, 2 years old dog outside in full sun without water on a 95 °F (35 °C) day without risking sunburn/heatstroke/etc.?

Clarify from comment posted by OP:
a dog was kept in that situation for an hour and a half, got into a debate about whether that was too long and went looking for sources for backup but none give a time limit. Argument was "well you take a dog to the beach, right?"

The dog needs shade and access to fresh water. If you see this situation - report it to the authorities and don't waste time and take the dog some water or remove it to a safe place.
– Yvette♦Aug 4 '17 at 8:30

Yes, OP was saying a dog was kept in that situation for an hour and a half, got into a debate about whether that was too long and went looking for sources for backup but none give a time limit. Argument was "well you take a dog to the beach, right?"
– 2nd_InquisitionAug 25 '17 at 11:41